Flower box support



FIG. 1 is a perspective view of a flower box support showing my new design, the broken-line depiction of a flower box being for illustrative purposes only and forming no part of the claimed design;

FIG. 2 is a right side elevational view thereof, the left side being a mirror image of that shown;

FIG. 3 is a rear elevational view thereof;

FIG. 4 is a top plan view thereof; and

FIG. 5 is a bottom plan view thereof. 

The ornamental design for a flower box support, as shown and described. 